1. Field of the Invention
A technique disclosed in the present specification relates to a semiconductor device including a heat dissipation member.
2. Description of Related Art
In order to improve a short circuit capacity of a semiconductor device, a semiconductor device including a heat dissipation member is developed (for example, Japanese Patent Application Publication No. 2007-110002 (JP 2007-110002 A)). In the semiconductor device in JP 2007-110002 A, an IGBT (Insulated Gate Bipolar Transistor) is formed in an element region of a semiconductor substrate. An emitter electrode is formed on a top surface of the semiconductor substrate, and a heat spreader (a heat dissipation member) is disposed on a top surface of the emitter electrode. In an element region (a central part of the element region) below the heat spreader, a space between unit cells of the IGBT is narrowed, and in an element region (an outer peripheral part of the element region) around the heat spreader, a space between unit cells of the IGBT is made wide. Hereby, a current density of the outer peripheral part of the element region is smaller than a current density of the central part. This makes it possible to stably restrain a temperature increase of the semiconductor device in short-circuit of the semiconductor device, thereby making it possible to improve a short circuit capacity.
In the semiconductor device in JP 2007-110002 A, the space between the unit cells of the IGBT is made wide in the outer peripheral part of the element region. That is, a space between trench gate electrodes is wide in the outer peripheral part of the element region. This easily causes electric field concentration in tips of the trench gate electrodes in the outer peripheral part, which may decrease a withstanding voltage of the semiconductor device.
Note that the paragraph [0015] of JP 2007-110002 A suggests that a channel density of the outer peripheral part is reduced by not forming an emitter region in some unit cells placed in the outer peripheral part, without changing the space between the unit cells. However, in such a technique, a current flows only to part (a trench gate electrode where an emitter region is formed) of the outer peripheral part, which may cause a current density thereof to be excessive.